The present invention relates to a system and method for managing slurry that is, for example, used when cutting workpieces with wire saws. More particularly, the present invention relates to slurry managing systems and slurry managing methods that enable optimal separation of impurities from used slurry.
A wire saw is typically employed to cut workpieces, such as silicon ingots, into wafers. The wire saw includes a plurality of rollers and a single strand of wire, which is spirally wound about the rollers with a predetermined pitch between each winding. The wire is guided by the rotation of the rollers. During rotation of the rollers, slurry containing abrasive grains is fed to the wire. In this state, a workpiece is pressed against the wire to cut the workpiece into a plurality of wafers simultaneously.
The slurry is an aqueous or oleaginous liquid (dispersion liquid) that contains abrasive grains. The wire saw is provided with a managing system to prepare and manage the slurry. The managing system includes a preparation tank, in which the abrasive grains and dispersion liquid are mixed to prepare the slurry. The slurry prepared in the preparation tank is fed to the wire saw.
It is preferred that the used slurry be recycled to reduce the costs of cutting the workpieces. However, used slurry includes impurities, which are fine grain components that are smaller than the abrasive grains. More specifically, the used slurry includes impurities such as cutting chips, produced during cutting of workpieces, and fragmented abrasive grains. The impurities decrease the cutting capability of the wire saw.
The managing system includes a separating apparatus that separates the impurities from the used slurry and recovers the recyclable abrasive grains and dispersion liquid. The separating apparatus has a first centrifugal separator for centrifugally separating turbid dispersion liquid, which includes impurities, from the used slurry to recover recyclable abrasive grains, and a second centrifugal separator for centrifugally separating impurities from the turbid dispersion liquid to recover recyclable dispersion liquid. The recovered abrasive grains and dispersion liquid are returned to the preparation tank to be prepared as slurry again. The slurry is then fed to the wire saw from the preparation tank and thus recycled.
Fluctuations in the temperature of the used slurry or in the amount of impurities included in the used slurry change the properties of the used slurry (e.g., specific gravity or viscosity). The changes in the properties of the used slurry alter the separating efficiency of the first and second centrifugal separators. This may hinder sufficient recovery of the abrasive grains and dispersion liquid from the used slurry or result in residual impurities left in the recovered abrasive grains and dispersion liquid.